In vehicles, it is becoming increasingly common to equip air conditioning systems with at least one additional evaporator in order to be able, for example, to cool separately at the front and rear or on the left and right side of the interior of the vehicle. To avoid unnecessary power consumption, it is desirable to be able to switch off the additional evaporators when there is no requirement. Use is therefore made of expansion valves comprising a shut-off device, which, in a closing position, closes a coolant inlet opening connected to a condenser and a coolant outlet opening connected to a compressor.
Valve arrangements in an expansion valve have already been disclosed, comprising a conical valve seat in which, in a closing position, a valve-closing member configured as a ball fits snugly in a closing position. Such thermostatic expansion valves are controlled by means of an actuating device, which, for the opening and closing of the valve arrangement, acts upon a transfer pin, which, by a lift motion, transports the valve-closing member out of a closing position in the valve seat into an opening position.
The previously known conical valve seats for receiving a spherical valve-closing member have the drawback that, directly after the valve arrangement is opened, a strong increase in mass flow volume is given by the obtuse angle of the valve seat faces. In order to obtain a fine regulation, an acute angle arrangement of the valve seat faces is necessary. These have the drawback, however, that, in order to induce an opening motion of the valve-closing member, it is necessary to overcome a self-locking mechanism.